Ok, I convinced my buddy to run his brand new Weiand 671 kit as is, which will make 11-12 psi boost according to some help I got here. To run this on pump gas and have it live I need suggestions on the lower end. Using a 350 block is a 4 bolt block necessary or good insurance? Same with the steel crank? Steel hub or balancer? He will get the crank machined for the full length keyway. He will be buying blower pistons and using some form of 70s factory head, probably 76CC chambers. Any suggestions on anything to make this live and perform decently? Now he wants to put it in a 70 nova with an automatic trans, where would you pull vacuum for the modulator? Also recommended here was boost referenced carbs, what is needed for that and how does it work? He will run two 650 or 750 holley double pumpers. Newbie questions but I will be getting one next year so I need the info too :)

To run that kind of boost you will need forged pistons, forged crank, good rods, etc... I don't think you understand the amount of power that it is going to make. You need good parts, a 2 bolt block splayed into a 4 bolt is the strongest way to go. At the very least you need a factory 4 bolt block.

As far as balancer/crank hub, keyway you need to work with your machinist and blower shop to figure out what they suggest. There are varying opinions on many of these things. If you don;t already have a crank you can get a small block crank with a big block snout, in that case a balancer would be the way to go.

I don't understand the head choice at all. Why put thousands of dollars into an engine and then slap so-so heads on it? Sure a blower will make power, but you need flow as well. Most of the GM 76cc heads are light weight castings, they will not be happy with the abuse the blower is going to dish out (heat). Those heads would be fine if you were talking 6lbs of boost. You might even make more boost with the 76cc GM heads, but you won't make as much power as a free flowing set of heads. You don;t need top of the line heads because the blower is going to move air, but you do need decent heads.

You will make power either way and plenty of it. You will have vacuum for the modulator under the carb base (above the blower). This is the same reason you need boost referenced carbs. On a N/A engine the vacuum drops as you open the throttle, which in turn opens the power valves (Holleys). With a blower the vacuum is not going to drop under the carb (at least not drop low enough), the blower will be pulling air through there as long as the car is running. Anyway, if you don't have boost referenced carbs it is VERY possible with higher boost applications to have the power valves not open and the engine run lean, this is a VERY BAD thing with a blower, lean is to be avoided at all times.

You and your friend should read this book "Street Supercharging' by SA Designs before going any deeper into it. This book is not the law, but it will give you a decent amount of knowledge to figure out which direction you want to go. There are many different ways to build a blown engine (just like N/A engines), you can go from mild to wild.

Good advice.

A complete parts list for my blown small block is on my web page below.

Listen to Royce and Jim, they both have very well thought out blower motor builds.

My build is listed below.

Forged pistons and good rod bolts are essential. Steel crank, 4-bolt mains, and better rods are a very good idea for the higher boost levels, above 8 or 10lbs. Look on both the BDS and Dyers sites..they give lots of advice on motor builds. Regarding the off the shelf Weiand kits you buy from Summit, I beleive they are set up for 7-9 pounds of boost and I think will need to buy an optional smaller top pulley to actually see 12 pounds on a 350ci. Dont forget fuel and boost guages to keep track of things.

mike